S.Y. Lee, IU

Design and Performance Expectation of ALPHA accelerator

S.Y. Lee, IU

2/26/2009

1. Introduction

2. Possible CIS re
-
build and parameters

3. Issues in the Design of a small electron Synchrotron.

4. Compact photon source

5. Accelerator parameters and performance expectation

Problems of CRANE Linac in Radiation effect experiments:

–
Parameter


Requirement


Goal


–
Dose Rate


1E12 rads/sec

5E12 rads/sec


–
Pulse width (narrow)


10
-

50 nsec

5
-

100 nsec


–
Pulse width (wide)


` 1
-

5 usec


1
-

10 usec


–
Beam spot size (85% uniformity)

40 mm

(diam)

65 mm (diam)


–
Pulse rep rate


10 shots/sec

50 shots/sec


–
Energy


40

-

60 MeV

–
No RF spikes in beam on target

–
Bremstrahlung Mode 2
?¦

3 cal/cm2

Our goal is to design a machine that can provide beam debunching,
beam accumulation for radiation effect experiments and generate X
-
ray photons for future applications for both CRANE NSWC and IU
Science Communities.

CIS: Circumference =17.364 m, Inj KE= 7 MeV, extraction: 240 MeV


Dipole length = 2 m, 90 degree bend, edge angle = 12 deg.

ALPHA:
No constraint on circumference (C=20m). Use CIS dipoles &
cavity; Need Damping wigglers, chicane, electrostatic kickers & septum

Using a single quadrupole
as in the DBA

Not a good idea!

1.
Quadrupole does not work

2.
How about Robinson wiggler?
–

not effective in changing J
x


3.
Gradient Damping wiggler

a.
Maximize straight section so that there are space for future applications

b.
Make it easy to operate

c.
C=20 m, B
1
/B
0
=1.9 m
-
1
. (AGS: B
1
/B
0
=4.1 m
-
1

)

Damping wiggler

Chicane for laser
-
electron interaction

cavity

Lambertson

septum

Injection kickers

Pulse from
linac

Extracted beam

Lambertson septum

Kicker 1

Kicker2

1.
Beam in and out in one
revolution satisfies the
CRANE requirement of
steady state

experiment.

2.
The accelerator can
accumulate
250 nC

of
charge in 10 or more
turns and extracted in one
turn for
transient mode

experiment (15J).

Debunch in 1 revolution






3
0
10
5
|
|




linac
Note that a large compaction factor is
necessary for achieving de
-
bunching
for the electron beams in a single path!

DBA

ε
=7.8nm

α
c
=0.15

Effect of the gradient damping wigglers

2
0
4
.
0









W
W
P
P

Location of Bumpers

Dynamic Aperture

2
0
2
0
3
3
0
0










Emittance and damping time!

Vacuum

energy.

of
function

a

as

emittance

m
equilibriu

the
calculate
can

we
,
2
.
9
25MeV,
for

9
.
48

Choosing
)
nTorr
(
)
/
(
)
/
(
:
emittance

m
equilibriu

The

CO

40%

H

60%

:
n
compositio

Vacuum
n
compositio


vacuum
on the

depends

:
g
pressure.

vacuum
:
P
emission.
photon

to
due

excitation

quantum

:
G
time.
damping

:
where
,
2
1
2
:
equation
evolution

emittance

The
dilution.

emittance

of

source
another

is

scattering

gas

Beam
1
0
5
0
1
0
2
0
2
m
g
P
g
gP
G
dt
d
g




















Emittances are dominated by pressure in low energy,

become natural emittances at high energy.

Touschek lifetime


Toucheck lifetime is sensitive
to the parameter:





is the rf bucket height,


is the horizontal momentum
spread


can range from 0.001 to 1.




we will need a lifetime of 1h


or more.




It can also be varied by
changing the momentum
compaction factor



In summary, the ALPHA
-
project includes:


I: Put back CIS with 2 electrostatic kickers and one
Lambertson

magnet, install
a surplus linac to demonstrate the single
-
turn injection and extraction scheme.

II: Refurbish and Install
CIS cavity
. Construct and install
damping wigglers
to
verify the momentum compaction factor tuning and 10 or more turn
accumulation! Commissioning the storage ring.

III: Build an injector LINAC for beam injection into the storage ring. In the
future, one can Move CRANE Linac to IUCF for high intensity beam
commissioning.

For eCIS design, the technology is well understood! The goal for the CRANE
radiation effect experiments can easily be met!

For the Compact Photon Source, the technology of 100 MW laser is available!

IV: 90MHz cavity for photon source development, Design of Laser system,
Optimization of Laser
-
beam interaction, photon flux and brilliance.

Accelerator Physics research
with the ALPHA storage ring:


1.
Quasi
-
isochronous accelerator
beam dynamics (
1
st

and 2
nd

order
compaction factors)

2.
Touschek Lifetime


3.
Nonlinear beam dynamics


4.
CSR


5.
X
-
ray: Electron beams in an infinitely
long linac (
α
c
=0), encountering
infinitely long weak undulators. What
will be the electron beam distribution?